For the past several years, the Environmental Protection Agency has had regulations to limit the amount of fuel vapor released into the atmosphere during the refueling of a motor vehicle. During a conventional or standard fueling operation, incoming fuel displaces fuel vapor from the head space of a fuel tank and out through the filler pipe into the atmosphere if not contained and recovered. The air pollution resulting from this situation is undesirable. Currently, many fuel dispensing pumps at service stations are equipped with vapor recovery systems that collect fuel vapor vented from the fuel tank filler pipe during the fueling operation and transfer the vapor to a fuel storage tank.
Recently, onboard, or vehicle carried, fuel vapor recovery and storage systems (commonly referred to as onboard recovery vapor recovery or ORVR) have been developed in which the head space in the vehicle fuel tank is vented through an activated charcoal-filled canister so that the vapor is adsorbed by the activated charcoal. Subsequently, the fuel vapor is withdrawn from the canister into the engine intake manifold for mixture and combustion with the normal fuel and air mixture. The fuel tank head space must be vented to enable fuel to be withdrawn from the tank during vehicle operation.
In typical ORVR systems, a canister outlet is connected to the intake manifold of the vehicle engine through a normally closed purge valve. The canister is intermittently subjected to the intake manifold vacuum with the opening and closing of the purge valve between the canister and intake manifold. A computer which monitors various vehicle operating conditions controls the opening and closing of the purge valve to assure that the fuel mixture established by the fuel injection system is not overly enriched by the addition of fuel vapor from the canister to the mixture.
Fuel dispensing systems having vacuum assisted vapor recovery capability which are unable to detect ORVR systems will continue to operate even though there is no need to do. This can waste energy, increase wear and tear, ingest excessive air into the underground storage tank and cause excessive pressure buildup in the underground storage tank due to the expanded volume of hydrocarbon saturated air. Recognizing an ORVR system and adjusting the fuel dispenser's vapor recovery system accordingly eliminates the redundancy associated with operating two vapor recovery systems for one fueling operation. The problem of incompatibility of assisted vapor recovery and ORVR was discussed in "Estimated Hydrocarbon Emissions of Phase II and Onboard Vapor Recovery Systems" dated Apr. 12, 1994, amended May 24, 1994, by the California Air Resources Board. That paper suggests the use of a "smart" interface on a nozzle to detect an ORVR vehicle and close one vapor intake valve on the nozzle when an ORVR vehicle is being filled.
Adjusting the fuel dispenser's vapor recovery system will mitigate fugitive emissions by reducing underground tank pressure. Reducing underground tank pressure minimizes the "breathing" associated with pressure differentials between the underground tank and ambient pressure levels. If the vacuum created by the fuel dispenser's vapor recovery system is not reduced or shut off, the underground tank pressure will increase to the extent that hydrocarbons are released through a pressure vacuum valve or breathing cap associated with the underground tank. In certain applications, reducing the vacuum created by the fuel dispenser's vapor recovery system when an ORVR system is detected permits the ingestion of a volume of air into the underground tank. When saturated with hydrocarbons, the volume of air expands to a volume approximately equal to the volume of fuel dispensed. Adjusting the fuel dispenser's vapor recovery system in this manner minimizes breathing losses associated with the underground tank.
A system and method for doing so is disclosed in commonly assigned U.S. Pat. No. 5,782,275 the disclosure of which is incorporated herein by reference. If the apparatus of the '275 patent detects an onboard system, it could either shut off the vapor pump completely, or control the pump to supply the amount of air to the storage tank needed to replenish the volume of liquid taken from the underground tank and thus eliminate breathing losses. The apparatus of the '275 patent includes a hydrocarbon sensor mounted in the vapor return passage of the hose used to fuel the vehicle. Further developmental work on the concept of hydrocarbon vapor sensing has revealed that the optimal point for monitoring the hydrocarbon concentration of vapors returning to the underground fuel tank may be within the dispenser.
There are potential difficulties associated with mounting a hydrocarbon sensor in the vapor return path of coaxial fuel delivery hose. These difficulties include addressing fire safety code requirements for an intrinsically safe device and routing sensor wiring through the hose. Moreover, dispenser hoses are equipped with "break away" fittings designed to cope with consumers who drive away from dispensers with a nozzle still in the vehicle fill pipe. Any type of wiring within the hose would have to be designed to be severable without generating a spark that could cause fire. Solving these technical problems could be expensive; accordingly, it would be advantageous to use a less expensive option.
The present invention addresses these and other problems as discussed in detail below. It should be recognized that the present invention provides numerous advantages some of which may not be detailed herein but which will be readily apparent to one of ordinary skill.